FIG. 1 shows the writing tip portion of a conventional ball point pen with the actual ball point and ink chamber 10 shown in outline and showing a distal end 12 of the retraction/protraction mechanism 14. The outer barrel or shell 16 has a distal end 18 received on a reduced diameter portion 20 of a conventional tip 22. In the more expensive types of pens, the outer shell 16 is generally formed of a relatively high priced metal, such as silver or gold, or a silver or gold plated metal, to provide an aesthetically pleasing writing instrument and tip 22 serves to protect the distal end portion 18 of the shell from damage. Typically, mechanism 14 is formed with an internal or female thread 24 which mates with external or male thread 26 provided on the reduced diameter portion 20 and tip 22 is threaded into mechanism 14 thereby locking shell 16 in its seat.
In the event that the retraction/protraction mechanism 14 fails and, if no glue was placed on threaded portion 26, the outer tip 22 can be unscrewed to release the mechanism and shell so that the old mechanism can be removed and replaced with a new one. Although this arrangement performs satisfactorily from an operational standpoint there is a desire to improve the aesthetics of the pen by extending the outer shell over essentially the entire length of the pen. This has been done, for example, as shown in FIG. 2 where shell 36 extends all the way to the distal end of the pen. However, this arrangement has several disadvantages. Shell 36 is generally too thin to provide any screw threads so that conventionally an extension 38 having an external threaded portion 40 is threaded into threaded portion 12 of retraction/protraction mechanism 14 and a generally frustoconical surface portion 42 having a shape generally matching that of shell 36 is attached to the shell by adhesive. Thus once the pen is assembled mechanism 14 is permanently locked into the pen so that if the mechanism fails the pen is not repairable. This is undesirable particularly since the mechanism is generally only a fraction of the cost of the gold or silver shell. The FIG. 2 structure has a further disadvantage in that the distal end portion 44 is unprotected and exposed to damage. Conventional gold or silver plating can more easily wear off at the end thereby exposing the base metal and adversely affecting the appearance of the pen.
Another limitation of conventional writing instruments relates to the clip which is generally mounted at the opposite end of the instrument. Typically, such clips have a flexible arm attached at one end to the shell, or cap if one is provided, with the opposite end biased against the respective shell or cap. The bias force tends to decrease with age thereby increasing the possibility of having the instrument dislodged from one's pocket resulting in losing the instrument.